Radio frequency (RF) semiconductor devices are changing to match the needs of increasingly innovative wireless standards. Signal bandwidths and carrier frequencies supporting greater data throughput rates are increasing over the time. This translates into increasingly complex devices, all of which need to be tested over wider operating ranges. Increased unit counts and multiple production lots are also needed to facilitate statistical correlation.
Signal integrity is the primary criteria in choosing a testing solution for RF device testing.
Many of the current solutions for testing of RF devices find it difficult to meet the required signal integrity due to various factors including the type and length of the contact used. Test contacting solutions using spring probes, which are vertical in connection comes with a longer contact, or conduction, length. The spring probe also comprises a multiple element assembly and this, along with the longer contact length, affects the signal integrity in a negative way.
Another important consideration is the length of the imprint. The length of the imprint is the summation of the length of the contact patch of the contact pin with the contact pad of the device being tested, and the wiping stroke. For very small or irregular sized contact pads, such as corner chamfer or dimple pads, it is crucial to have a short imprint. Solutions such as U.S. Pat. No. 7,819,672 (Osato) have long wiping strokes, which translates into long imprints, and is unsuitable for short or irregular contact pads.
In general, having longer contact pins used in the testing apparatus translates into poorer signal integrity. Also, having a shorter imprint allows testing of devices with smaller contact pads, as well as irregular contact pads as in the case of corner chamfer and dimple pads.
Electrical contacts with short imprints are available, such as that taught in U.S. application Ser. No. 14/855,341 (Foong, et. al.), which is the parent to this current application. One issue with the design taught in that application is the tendency for the contact pins to drop, as is the case for most single elastomer designs. Another issue of that design is that the rectangular elastomer has the propensity to deform over time, which in turn causes a loss of opposing force when compressed.
What is needed in the art is a RF device testing apparatus that maintains good signal integrity and is able to test devices with very small contact pads, or atypically shaped pads such as in corner chamfer and dimple pads, and at the same time preventing dropping of contact pins during assembly and providing a good opposing force to compression for a longer time.